(or reverse area), a hysteresis of 2° is added. This hysteresis prevents chattering of the directional result. The
current vector reaches the forward area at ±84° (= 86°-2° hysteresis).
[7sj6x_vorwaertscharakteristik-gumz-phase-220904-he, 1, en_US]
Figure 2-27 Forward characteristic of the directional function, directional phase element
Direction Determination of Directional Ground Element with Ground Values
Figure 2-28 shows the treatment of the reference voltage for the directional ground element, also based on a
single-phase ground fault in phase A. Contrary to the directional phase elements, which work with the
unfaulted voltage as reference voltage, the fault voltage itself is the reference voltage for the directional
ground element. Depending on the connection of the voltage transformer, this is the voltage 3V
0
(as shown in
Figure 2-28) or V
N
. The fault current -3Ι
0
is phase offset by 180° to the fault current Ι
scA
and follows the fault
voltage 3V
0
by fault angle ϕ
sc
. The reference voltage is rotated by the setting value 1619 ROTATION ANGLE.
In this case, a rotation by -45°.
[7sj6x_drehung-referenzspannung-erde-nullsys-220904-he, 1, en_US]
Figure 2-28 Rotation of the reference voltage, directional ground element with zero sequence values
The forward area is also a range of ±86° around the rotated reference voltage V
ref, rot
. If the vector of the fault
current -Ι
0
(or Ι
N
) is in this area, the device detects forward direction.
Direction Determination of Directional Ground Element with Negative Sequence Values
Figure 2-29 shows the treatment of the reference voltage for the directional ground element using the nega-
tive sequence values based on a single-phase ground fault in phase A. As reference voltage, the negative
Functions
2.3 Directional Overcurrent Protection 67, 67N
SIPROTEC 4, 7SJ80, Manual 93
E50417-G1140-C343-A8, Edition 12.2017
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